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You use them when there are 2 fractions with different denominators.

Q: When do you have to use the common denominators?

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If the denominators are not the same, then you have to use equivalent fractions which do have a common denominator . To do this, you need to find the least common multiple (LCM) of the two denominators. To add fractions with unlike denominators, rename the fractions with a common denominator.

multiply the denominators

Every set of denominators has a common denominator, even if it's only their product.

When you're adding or subtracting fractions with different denominators, if you multiply the denominators that's your Quick Common Denominator. I'ts useful for denominators that don't have a low Least Common Factor.

By finding the lowest common multiple of the different denominators then rearranging the numerators and denominators accordingly.

Related questions

If the denominators are not the same, then you have to use equivalent fractions which do have a common denominator . To do this, you need to find the least common multiple (LCM) of the two denominators.

If the denominators are not the same, then you have to use equivalent fractions which do have a common denominator . To do this, you need to find the least common multiple (LCM) of the two denominators. To add fractions with unlike denominators, rename the fractions with a common denominator.

Common multiples and common denominators can be found using the same process. They differ in their function. Common denominators are common multiples that are functioning as denominators.

Common denominators are common multiples of two or more denominators.

Denominators which have no common factors

There are an unlimited number of common denominators if you want to use ridiculously large numbers. There is ONLY ONE Least Common Denominator (LCD, LCM).

The least common denominator is the least common multiple of the denominators.

multiply the denominators

probably to multiply easier

The least common multiple of the denominators is knows as the LCD or least common denominator.

Denominators. This is where the term, common denominators comes from.

Multiply them by each other.